Despite influential findings regarding early reading development and prevention approaches for students with reading disabilities, many students with reading disabilities demonstrate inadequate reading comprehension in the middle grades, affecting learning which bodes unfavorably for post secondary outcomes. Project 3 is designed to address 3 aims that build on the findings from the previous 5 years of research (Vaughn & Fletcher, in press) with struggling readers in grades 6- 8, capitalizing on research from Projects 1 and 2 in the proposed studies, and providing samples for Project 4. Aim 1 determines the efficacy of reading comprehension interventions comparing outcomes of 4th graders with reading difficulties randomly assigning students (n=420) to typical classroom reading instruction or to one of two replacement interventions (Language/Knowledge or Skills/Strategies). Students will be treated for 2 years and then followed for one (through sixth grade). Aim 2 extends the first intervention study by building on the experimental studies conducted during years 1 and 2 by Project 2 (Executive Functioning), and conducting a second RCT with a nonoverlapping sample of 4th graders with reading difficulties assigned to one of two treatment conditions, hybrid from Year 1 or hybrid from Year 1 with executive functioning practices. Like students in the 1st study, these students will also be treated for two years (grades 4 and 5) and then followed through grade 6. Aim 3 determines student characteristics and contextual factors associated with response to intervention as a means of informing treatment decisions, and to determine the extent to which response to intervention can be predicted initially and longitudinally from students' characteristics (e.g., memory, motivation) and contextual factors (e.g., teachers' knowledge, school effectiveness ratings, neighborhoods access to literacy). Students will be assessed on efficacy impact measures including word reading, fluency, reading and listening comprehension, spelling, written expression, oral language and vocabulary. Students will also be assessed on student characteristics (e.g., working memory) and behavioral measures (e.g., self-regulation) as well as measures related to teacher and school context (e.g., classroom climate).